1. Field of the Invention
The present invention relates to a tachometer signal generating device for an engine used for, for instance, an outboard engine.
2. Discussion of Background
A conventional tachometer signal generating device is described with reference to FIG. 7 which shows a circuit diagram of such device.
In FIG. 7, the conventional tachometer signal generating device comprises a lighting coil 1 for a generator, a lamp 2 and a tachometer wherein the lamp 2 and the tachometer are respectively connected in parallel to the lighting coil 1.
In the operation of the conventional device to be mounted on an outboard engine, the tachometer 3 receives signals indicating the number revolution from the lighting coil 1 of the generator.
When a 4-pole generator is used, a signal of 2 cycles/one revolution is outputted from the lighting coil 1. When a 6-pole generator is used, a signal of 3 cycles/one revolution is outputted. Further, in a case of 12-pole generator, a signal of 6 cycles/one revolution is outputted. Accordingly, it was necessary to use a tachometer 3 which corresponds to the number of poles of the generator.
In the market for the outboard engine, tachometers generating a signal of 6 pulses/one revolution are generally commercialized. Accordingly, in a case of an outboard engine having a six-pole generator, a 3-pulse signal into a 6-pulse signal by using a device such as a signal multiplier circuit. And then, a tachometer for an input of a signal of 6 pulses/one revolution is used. Accordingly, there was a problem of increasing cost.
Conventionally, a tachometer applicable to a different number of poles was proposed. However, it requires a switching circuit for the different number of poles, and the construction is complicated. Thus, there was a problem of cost increase.